This invention relates generally to methods for suppressing mechanical vibration and mechanical impact shocks, and more particularly relates to materials and structures for suppressing mechanical vibration and impact shocks.
The suppression of mechanical vibration noise and impact shocks by mechanical damping is a widely sought property in materials, not only as a matter of scientific interest, but also to enable new technologies. A wide range of proposed mechanical and electromechanical systems ranging in dimension from the macro-scale to the meso-scale, micro-scale, and even nano-scale, critically rely on at least minimal suppression of vibration and impact shock to maintain integrity of system operation. Indeed, without vibration suppression or mechanical isolation, many complicated mechanical systems can malfunction or be damaged, or demonstrate only suboptimal operational performance.
One class of materials, shape memory alloys (SMAs), have been shown to demonstrate mechanical damping in macro-scale systems. Shape memory alloys undergo reversible transformations between two distinct morphological phases in response to changes in temperature or applied stress. It has been shown in macro-scale SMA structures that the creation and motion of the internal interfaces between these two phases during such transformations dissipates energy, providing mechanical damping of the mechanical system in which a macro-scale SMA structure is employed.
But for many mechanical systems, conventional macro-scale damping structures are not effective or even applicable. For example, improved mechanical damping is presently of interest in micro electromechanical systems (MEMS), which are generally based on microelectronic materials and planar microfabrication technology, and which for many applications are required to mechanically operate for hundreds of millions, or even billions, of mechanical cycles without failure. Such micro-scale systems, as well as nano-scale systems, are not in general amenable to conventional damping structures.
Yet while damping and fatigue characteristics are of paramount importance for MEMS, these properties are often on opposite sides of a trade-off. For example, by packaging a MEMS structure in air or exposed to ambient air, an air squeeze film can be formed that can contribute to damping of spurious mechanical vibrations in the structure or the immediate surroundings. But silicon MEMS structures can fatigue through an oxidation mechanism during air exposure. The resulting oxidation fatigue can be alleviated by vacuum packaging, but this is found to exacerbate the transmission of mechanical shock and noise to MEMS components from their use environment. Endurance against hazardous environmental vibrations is therefore correspondingly reduced by a vacuum package. Thus, one of either structural integrity or mechanical operation performance often must be compromised in favor of the other in advanced sensing and actuating MEMS technologies.
This example demonstrates that for many mechanical systems, across a range of dimensions, mechanical damping requirements can often not be well-addressed without a required compromise in protection against environmental conditions, without limits on operational performance, precision, or reliability, or without prejudicing another consideration in the success of the system. Conventional mechanical damping configurations have heretofore necessitated such compromises and as a result have limited the applications of mechanical systems in the meso-scale, micro-scale, and nano-scale regimes.